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Award Ceremony Speech

On 12th December 1901, Marconi succeeded in establishing wireless
communication between the Old World and the New. The way in which
the wireless waves proved to follow the contour of the earth
compelled the assumption that there must be an electrically
conducting layer somewhere high up in the stratosphere. Thereby,
it was thought, the linearly moving radio waves were thrown back
towards the earth just as the rays of the sun are deviated so
that its light can be observed long after the sun has passed
below the horizon. According to Heaviside and Kennelly such a
layer which throws back the radio waves and girdles the whole
earth conceivably be due to the ionizing effects of the
ultraviolet rays of the sun on the upper atmosphere. However, no
conclusive proof of this was forthcoming even at the beginning of
the 1920's.

At this time the rapid development of radio, especially in
England and America, rendered the crowding of the ether so great
that amateurs had to be relegated to wavelengths below 100
metres, while the kilometre-long waves were then considered to be
most suitable for long-distance transmissions. The most immediate
difficulties for the amateurs were to obtain transmitters with
sufficient effect for the great distances. The competitions
arranged for amateurs in radio signalling with short waves
between America and Europe in the years 1921 and 1922 proved,
however, that in sporadic cases communication could be obtained
with surprisingly small transmitter effect.

It was here that Appleton's contributions now began to make
themselves felt. By means of a brilliantly worked-out method, the
so-called frequency variation method, in 1924 together
with Barnett, he showed that there was interference between the
direct radio waves along the ground and a wave reflected towards
the layer in space, and that this so-called Heaviside
layer is at about a height of 100 km. By means of a fine
theoretical analysis of the penetration of the wave into the
layer, Appleton was also able to investigate certain important
detail phenomena which were observed in connection with these
investigations. Thus the wave was refracted in the layer in the
same way as a ray of light entering an optically thin medium.
Consequently radio waves will either be thrown back towards the
earth or, if they are strong enough to penetrate to the middle of
the layer where the ionization is greatest, they will rum through
it and out into space. According to the theory from the critical
wavelength at which this takes place can be read off the
ionization at different points of the stratosphere, often at
great distances from the transmitter. During the last World War,
stations with equipment for registering these conditions were
established in different parts of the earth's surface.
Information from these stations is of great importance for radio
communication, as it affords guidance in the choice of the
wavelength which should be selected in the case of radio
communications between two places. But, as we shall see
presently, these investigations are of considerable importance
for many other things besides radio communication.

It was in the course of the study of these phenomena that
Appleton found in 1927 that there must exist still another
reflecting layer beyond the one mentioned previously, at a height
of about 230 km. This so-called Appleton layer is still
more exposed to the ultraviolet solar radiation than the
underlying layer, or more correctly: the underlying layers, for a
further couple of layers of more or less sporadic occurrence,
have been proved in the course of time. Ionization is therefore
more complete up there than in the underlying layers, and there
is a greater power of reflection against the radio waves.
Appleton has shown that during the day the new layer is divided
into two components which again merge into one during the night.
It is mainly the upper layer which, owing to its greater capacity
of reflection, facilitates radio communications. In another
respect also it differs from the lower layers. While in the
latter the ionization constantly follows the changes in the
ultraviolet solar radiation, the upper Appleton layer remains
unchanged during the greater part of the night. This is explained
by the great rarefaction prevailing at these heights, which
retards the recombination of the ions of the air. The close
correlation exhibited by the ionization of the lower layers with
the changes in the ultraviolet solar radiation was convincingly
shown by Appleton's observations between the time of the minimum
of sunspots in 1934 and that of the maximum of sunspots in 1937.
The increase in the ionization then amounted to 50 to 60%,
corresponding to an increase in the intensity of the sun's
ultraviolet radiation of 120 to 150%. This circumstance is so
much the more remarkable as observations made on the surface of
the earth during the same period show that the ultraviolet
radiation there was practically unchanged. Thus the radio method
has proved to be a means of determining the actual radiation of
the sun. Through the sunspots, which must be looked upon rather
as holes or windows opening into the interior of the sun, we
observe some - of the mighty processes taking place there.
Appleton has also found that the disturbances, which, in the form
of short radio waves, emanate from these sunspots are equivalent
to transmitter effects of millions of kilowatts.

It would carry us too far to give a detailed account here of all
the discoveries and investigations which we have owed to Appleton
during the last few years. I shall only dwell briefly upon one
aspect of them. The echo methods which were developed by Appleton
and his co-workers in the years before the World War must be
looked upon as precursors of the radar methods which were
so successfully employed by the Allies during the War for
locating aeroplanes, submarines, etc. The ultrashort radar waves,
3-30 cm in length, will certainly be employed for many purposes
in the immediate future, inter alia as an important
auxiliary aid within meteorology. The direction of radar
waves is not changed during their passage through ionized layers,
but they are changed owing to the inhomogeneities arising owing
to variations in the pressure and temperature of the air and its
varying content of aqueous vapour. Thus the radar waves are
reflected by showers, which can be detected at far distances and
determined by the radar echo. During the World War radar methods
were extensively used to locate the heat front and the cold front
in distant low-pressure areas.

Finally, it may be mentioned that Appleton has carried out
far-reaching investigations of the electric waves which are
produced when the lightning strikes. With the help of specially
equipped sounding stations, lightning discharges and
thunderstorms which are 1,000 to 2,000 km away can be located,
and the disturbances which affect radio reception he has found to
be due to interplay between far-distant thunderstorms, especially
on the equator.

Thanks to Appleton's contributions a new branch has been added to
physical science, but not only that: the methods which he and his
co-workers have perfected to investigate the atmosphere round the
earth by means of radio waves have also become of immense
importance for solving problems within other sciences, such as
astronomy, geophysics and meteorology, and for radio
technics.

Sir Edward Appleton. Electromagnetic waves
are a subject of the greatest physical importance, and they are
being increasingly applied in different fields of science. The
first arguments on the existence of these waves were advanced
more than a hundred years ago by your countryman Michael Faraday,
who was then searching for the relations between optical and
electrical phenomena. His ideas were worked out in strict
mathematical equations by dames Clark Maxwell in 1873. The waves
were finally discovered by the famous German physicist Heinrich
Hertz in the early 1890's. Shortly afterwards their immense
usefulness as radio waves was demonstrated by the Italian
inventor Guglielmo
Marconi.

Since then, electromagnetic waves have advanced victoriously in a
multitude of sciences, giving rise, in the hands of men of
genius, to scientific methods and instruments, among which I need
only mention the electronic tube, based on the thermo-ionic laws,
so thoroughly investigated by Sir
Owen Richardson.

Now you have added a new link to this beautiful chain, applying
the waves to the study of our own atmosphere. With the aid of
these waves you have reached etherial regions never before
attained by man. You have even taught us how to listen to the
roar from eruptions in the sun and distant stars in the
galaxy.

The usefulness of radar waves as applied to the solution of
problems in meteorology has already been shown. The need for such
a refined and instantaneous control of the unreliable and
capricious conditions prevailing in the earth's atmosphere cannot
be overestimated, especially in respect to the risks which still
jeopardize aviation.

From Greek mythology we learn how Dacdalus fastened a pair of
wings to the shoulders of his son Icarus with wax. But Icarus
flew too near the sun, and the wax melted, so that he fell into
the sea and was drowned. Certainly the modern Icarus also needs
to strengthen his wings in his flights.

On behalf of the Royal Swedish Academy of Sciences I congratulate
you on your important discoveries, and I will now ask you to
receive your Nobel Prize from the hands of His Majesty.